WO 98/47271 describes a protocol processor for manipulating a stream of data supporting both, isochronous and asynchronous format data transfer. In a certain embodiment, an isochronous data pipe is used to act as virtual asynchronous data pipe, transmitting all asynchronous data to be transferred.
Data, which are transferred in an isochronous manner reach a target device at a predetermined time while data, which are transferred in an asynchronous manner do not necessarily reach a device at a predetermined time. If data, which is transferred in an isochronous manner does not reach its target device it is not resent in order not to delay following isochronous data. Data, which is transferred in an asynchronous manner is checked for its reception by the target device. If such data does not reach its target device it is resent until it is assured that it has reached its target device. Usually control commands are sent in an asynchronous manner in order to assure that the control command has reached its target device.
Control commands having different target devices are sent as different items, one for each target device. Control commands thus do not reach their respective target devices at the same time. This is regarded to be disadvantages in case that undesired effects occur when said control commands do not reach their target devices at the same time.